In order to protect an electrical load against an overload caused by an excessively high current, a fusible link can be connected in series with the load. Such a fuse triggers in accordance with a design-predetermined triggering characteristic curve if a current taken up by the load exceeds a predetermined limit value. Such a fuse also protects a voltage supply arrangement of the load against an overload if a short circuit occurs in the load. There are fuses in various fuse classes that differ with regard to the triggering criteria, i.e., the triggering current and the triggering delay. However due to manufacturing, fusible links are subject to considerable variations with regard to the triggering criteria, such that fuses of the same class can differ significantly with regard to the triggering current and the triggering delay.
Power transistors, such as, e.g., power MOSFETs, can be used as switches for electrical loads. So-called Smart-FETs, in particular, are suitable as switches for this purpose. Smart-FETs, such as, for example, PROFETs® from Infineon Technologies AG, Munich, are power MOSFETs having additional protection functions. One of these protection functions is an overload protection, which turns off the MOSFET if the load current thereof, for example due to a short circuit of a connected load, reaches a predetermined limit value. Another of the protection functions is an overvoltage protection, which activates the MOSFET if the drain-source voltage thereof reaches a predetermined limit value, in order to prevent a further voltage rise and to protect the component against damage. If the MOSFET is turned off owing to an overcurrent, then the overvoltage protection makes it possible to convert the electrical energy stored in inductive loads into heat. This energy is proportional to the product of the square of the load current that flowed last and the total inductance (E=L·I2).
What is problematic in this context is that, due to an advancing increase in the integration density, power MOSFETs with a given blocking voltage capability and given ampacity are becoming smaller and smaller, that is to say that the volume of a semiconductor chip in which the MOSFET is integrated and which takes up the waste heat is becoming smaller and smaller. With an advancing increase in the integration density, therefore, a given electrical energy to be converted into heat leads to a greater heating of the semiconductor chip. In this case, consideration should be given to the fact that a technology-dictated maximum temperature must not be exceeded, in order to avoid damage to the component.